The Integumentary System (Introduction) Two major parts of the integumentary system 1. Cutaneous membrane, or skin 2. Accessory structures Hair Exocrine glands Nails

Cutaneous Membrane (Introduction) Consists of two layers Superficial epithelium, or epidermis Underlying connective tissues of the dermis Hypodermis, or subcutaneous layer Loose connective tissue beneath the dermis Separates integument from deeper tissues Not part of the integumentary system, yet interwoven with connective tissue of the dermis

Figure 5-1 The General Structure of the Integumentary System.

Five General Functions of the Integument (Introduction) Protection Skin covers and protects underlying tissues Prevents fluid loss Temperature maintenance Skin regulates heat exchange with the environment Synthesis and storage of nutrients Epidermis synthesizes vitamin D3 Dermis stores lipids in adipose tissue

Five General Functions of the Integument cont. (Introduction) Sensory reception Receptors detect touch, pressure, pain, and temperature and relay information to nervous system Excretion and secretion Glands excrete salts, water, and organic wastes Specialized integumentary (mammary) glands secrete milk

The Epidermis (5-1) Composed of layered epithelial tissue Avascular (contains no blood vessels) Relies on diffusion from underlying connective tissue for nutrients and oxygen Deepest cells (closest to the dermis) are most active Cells in outer, superficial layers are dead Majority of the cells are keratinocytes Contain the protein keratin

Thick and Thin Skin (5-1) Terms “thick” and “thin” refer to thickness of epidermis (not whole integument) Thick skin – five layers of cells Found on palms of hands and soles of feet Very thick stratum corneum (outermost layer) Total thickness about 0.5 mm (standard paper towel) Thin skin – four layers of cells Covers the rest of the body Total thickness about 0.08 mm (plastic sandwich bag)

Figure 5-2a-b The Epidermis

Strata of the Epidermis (5-1) Five cell layers (strata) of thick skin from deep to superficial Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum Deep Superficial

Figure 5-2b The Epidermis

Stratum Basale (5-1) Deepest layer of the epidermis Attached to basement membrane by hemidesmosomes Cells in the stratum basale Basal cells Stem cells that continually divide to replace cells lost at the surface Merkel cells (sensitive to touch) Melanocytes (synthesize pigment melanin)

Epidermal Ridges (5-1) Formed by cells of the stratum basale extending down into dermis Dermal projections (dermal papillae) extend up into epidermis between ridges Ridges and papillae interlock Increasing surface area for diffusion Strengthening bond between layers Contours of skin surface follow ridge patterns Basis for fingerprints Figure 5-2a-e The Epidermis

Intermediate Strata (5-1) New daughter cells formed in stratum basale migrate upward toward skin surface Cells progress through three intermediate layers Stratum spinosum Stratum granulosum Stratum lucidum

Stratum Spinosum (5-1) Stratum spinosum (spiny layer) Cells may continue to divide Consists of keratinocytes held together by desmosomes Contains branched dendritic cells (involved in the immune response)

Stratum Granulosum and Stratum Lucidum (5-1) Stratum granulosum (grainy layer) Cells have stopped dividing Cells have started making keratin Durable, water-resistant protein Coats surface of skin and forms hair and nails Stratum lucidum (clear layer) Composed of flattened, densely packed cells filled with keratin

Stratum Corneum (5-1) Contains 15–30 layers of flattened, dead cells packed with keratin Called keratinized cells Cells tightly connected by desmosomes Because of connections, are generally shed in large groups or sheets

Cell Progression in the Epidermis (5-1) Generally takes 7–10 days for cell to move from stratum basale to stratum corneum In the process, cells fill with keratin and die Dead cells stay in the stratum corneum for two more weeks before being shed or washed away

Skin Color – Pigmentation (5-2) Carotene and melanin are the two pigments that influence skin color Carotene Orange-yellow pigment Accumulates in epidermal cells Found in orange-colored foods (carrots, squashes)

Skin Color – Pigmentation cont. (5-2) Two types of melanin, red-yellow and brown-black Made by melanocytes Store melanin in vesicles called melanosomes Activity increases in response to UV Melanin absorbs UV radiation, protecting deeper layers of epidermis and dermis

Figure 5-3 Melanocytes.

Dermal Circulation and Skin Color (5-2) Oxygenated blood is bright red Increase in body temperature dilates superficial blood vessels in dermis Result is a flushed, red skin color Temporary constriction of the same vessels results in pale skin Cyanosis, a bluish coloration, occurs when blood oxygen supplies are diminished

Beneficial Effects of Sunlight on Skin (5-3) Vitamin D3 Formed by epidermal cells Converted from a cholesterol steroid when epidermal cells exposed to sunlight Liver and kidneys convert vitamin D3 into calcitriol Essential for absorption of calcium and phosphorus Inadequate vitamin D3 can lead to weak and flexible bones

Detrimental Effects of Sunlight on Skin (5-3) Skin cancers Any cancer of epithelial tissue is a carcinoma Basal cell carcinoma is most common skin cancer Originates in stratum basale Squamous cell carcinoma found in more superficial layers Malignant melanoma is most dangerous Usually begins from a mole Can metastasize through the lymphatic system Figure 5-4 Skin Cancers.

The Dermis (5-4) Lies between the epidermis and hypodermis Contains two major layers Superficial papillary layer Deeper reticular layer

The Dermal Papillary Layer (5-4) Named after the dermal papillae Consists of areolar tissue Supports and nourishes epidermis Contains capillaries, lymphatic vessels, and sensory neurons supplying skin surface

The Dermal Reticular Layer (5-4) Interwoven meshwork of dense irregular connective tissue Elastic fibers provide flexibility Collagen fibers limit flexibility and so prevent damage to tissue Dominant cell type is fibroblast Accessory organs derived from epidermis (hair follicles, sweat glands) extend into this layer Also contains: blood vessels, lymphatic vessels, nerve fibers, and sensory receptors

Figure 5-1 The General Structure of the Integumentary System.

The Hypodermis (5-5) Also called the subcutaneous layer Deep to the dermis Fibers intermixed with dermis, so no clear delineation Not actually part of the integument But stabilizes position of the skin relative to underlying tissues Consists of areolar tissue with many fat cells No vital organs in area make it an ideal site for subcutaneous injections

Hair and Hair Follicles (5-6) Accessory structures of the integumentary system Hairs Nonliving, keratinized structures Produced by hair follicles Project above the skin surface everywhere except: The sides and soles of the feet, palms of the hands, sides of the fingers and toes, the lips, and portions of the external genitalia

Hair Follicle Structure (5-6) Project into dermis and usually into hypodermis Walls contain all cell layers found in epidermis Epithelium at the base of follicle forms cap over the hair papilla Connective tissue that contains capillaries and nerves Hair matrix surrounds hair papilla Contains epithelial stem cells Cells divide and push daughter cells toward surface

Figure 5-5b Hair Follicles and Hairs.

Hair Structure (5-6) As hair cells move toward surface, they become keratinized and die Point of keratinization is about halfway to skin surface and marks boundary between hair root and shaft Hair root – portion that anchors hair into skin Hair shaft – hair part we see on the surface

Hair Shaft Structure (5-6) Three layers of dead, keratinized cells Cuticle (surface layer) Made of an overlapping shingle-like layer of cells Contains hard keratin, giving hair stiffness Cortex – also contains hard keratin Medulla Makes up the core Contains flexible soft keratin

Figure 5-5c Hair Follicles and Hairs. Connective tissue sheath Wall of hair follicle Cuticle of hair Cortex of hair Medulla of hair C This cross section through a hair follicle was taken at the boundary between the hair shaft and hair root. Figure 5-5c Hair Follicles and Hairs.

Hair Growth (5-6) Hair growth cycle Grows for two to five years Follicle becomes inactive for same time frame When new growth cycle begins, follicle produces new hair Old hair gets pushed to surface and shed

Functions of Hair (5-6) Protects the scalp from UV light Provides insulation for the skull Prevents entry of foreign particles into nose, eyes, and ears Provides early-warning system to prevent injury due to sensory fibers at base of hair follicles Expresses emotional state by hair “standing up” due to contraction of arrector pili muscle Produces “goose bumps”

Hair Color (5-6) Differences due to type and amount of melanin from melanocytes Hair color varies from black to blond Genetically determined and influenced by hormones and environmental factors Pigment production declines with age causing gray or white hair

Exocrine Glands of the Skin (5-7) Two types of exocrine glands in the integument Sebaceous glands Sweat glands Figure 5-6 Sebaceous Glands and Their Relationship to Hair Follicles.

Sebaceous Glands (5-7) Also called oil glands Discharge oily lipid secretion (sebum) into hair follicles through holocrine secretion (cell dies and detaches) Sebum inhibits growth of bacteria, lubricates the hair, and conditions surrounding skin Sebaceous follicles discharge sebum directly onto skin of face, back, chest, nipples, and external genitalia

Sebaceous Glands and Acne (5-7) Sebaceous glands are sensitive to changes in concentrations of sex hormones Secretions accelerate at puberty Acne Blocked sebaceous ducts causes inflammation and raised “pimple”

Sweat Glands (5-7) Also called sudoriferous glands Include two types Apocrine Merocrine Figure 5-7 Sweat Glands.

Apocrine Sweat Glands (5-7) Become active at puberty Secrete into hair follicles in armpits, around nipples, and in pubic region Secretion is sticky, cloudy, and potentially odorous Portions of cell with secretions pinch off Sweat is food source for bacteria on skin, increasing odor

Merocrine Sweat Glands (5-7) Coiled tubular structure secretes watery perspiration directly onto surface of skin Very numerous with high numbers on soles and palms Sweat is 99 percent water with electrolytes, urea, and organic nutrients Sodium chloride gives it the salty taste Function is to cool body through evaporation

Modified Sweat Glands (5-7) Mammary glands Structurally related to apocrine sweat glands Secrete milk Ceruminous glands Located in passageway of external ear Secretions combine with sebaceous gland secretions to form cerumen, or earwax

Nails (5-8) Protect surfaces of tips of fingers and toes Visible nail body Made of dense, keratinized cells Recessed beneath surrounding epithelium Bordered by lateral nail folds Nail bed Deeper level of epidermis covered by nail body

Nail Structure (5-8) Nail root Lunula Epithelial fold not visible from the surface Site of nail production Covered by the cuticle Portion of the stratum corneum Lunula Pale crescent near nail root

Figure 5-8 The Structure of a Nail.

Repair of the Integument (5-9) Skin regeneration occurs because: Stem cells of epithelium and connective tissue undergo cell division Replacing lost or damaged tissue Four phases of skin regeneration Inflammatory phase Migratory phase Proliferation phase Scarring phase

Inflammatory Phase (5-9) Mast cells released at bleeding injury site trigger inflammatory response Result is increased blood flow to region and increased numbers of phagocytes Figure 5-9 Repair of Injury to the Skin.

Migratory Phase (5-9) Blood clot or scab forms at surface Stratum basale cells migrate along wound edges to replace missing cells More phagocytes clear debris and pathogens If wound covers extensive area or involves a region of thin skin: Granulation tissue forms in deeper tissue Combination of blood clot, fibroblasts, and extensive capillary network

Figure 5-9 Repair of Injury to the Skin. 2 Migratory Phase After several hours, a scab has formed and cells of the stratum basale are migrating along the edges of the wound. Phagocytic cells are removing debris, and more of these cells are arriving with the enhanced circulation in the area. Clotting around the edges of the affected area partially isolates the region. Migrating epithelial cells Macrophages and fibroblasts Granulation tissue Figure 5-9 Repair of Injury to the Skin.

Proliferation Phase (5-9) Deeper parts of the clot dissolve Number of capillaries declines Fibroblasts have formed extensive meshwork of collagen fibers Figure 5-9 Repair of Injury to the Skin.

Scarring Phase (5-9) Scab is shed and epidermis is complete Shallow depression marks injury site Fibroblasts create fibrous, noncellular scar tissue to elevate epidermis Degree of scar formation dependent on severity and location of injury and age of patient Keloids are thickened areas of scar tissue covered by shiny, smooth epidermal surface

Figure 5-9 Repair of Injury to the Skin. Figure 5-10 A Keloid.

Effects of Burns (5-9) Burns result from exposure of skin to heat, radiation, electrical shock, or strong chemicals Severity depends on depth into the tissues and the total area affected Skin functions affected by burns Fluid and electrolyte balance Thermoregulation Protection from infection

Classification by Depth of Burn (5-9) Partial-thickness burns First-degree burn Only the epidermis is affected Causes erythema or redness from inflammation Example: sunburn Second-degree burn Entire epidermis and part of the dermis damaged Causes blistering, pain, and swelling Some scar tissue may form

Unnumbered Figure, Page 136-1 & 2 Partial-thickness Burns Erythema Erythema

Unnumbered Figure, Page 136-3 Full-thickness Burns

Effects of Aging on the Integument (5-10) Skin injuries and infections are more common Likely due to a thinning of the epidermis as stem cells become less active Sensitivity of immune system is reduced Mainly due to a decrease of macrophages residing in the skin Muscles become weaker and bone strength decreases Due to a decline in vitamin D3

Effects of Aging on the Integument (5-10) Sensitivity to sun exposure increases Due to lower amount of melanin production Skin becomes dryer and often scaly Due to reduction in glandular secretions Hair thins and changes color Due to low-functioning follicles and decreased melanocyte activity

Effects of Aging on the Integument (5-10) Sagging and wrinkling of the skin occurs Due to decrease in elastic network, more noticeable when skin has been exposed to a lot of sunlight Ability to lose heat is reduced Due to reduced dermal blood supply and less active sweat glands Skin repairs take place more slowly Due to slower stem cell division, increasing the threat of infection in cuts